Dental amalgam remains the most common direct filling material for restoration of tooth structure. The presence of mercury in a material used in the oral cavity has raised some concerns. Although dental amalgam is considered safe, a reduction in the amount of released mercury is desirable, and is the overall goal of the project. The specific long-term objectives are to determine the mechanism of the release of mercury from dental amalgam restorations, and to find conditions, which result in the lowest possible release rate. The proposed work is based on a model of mercury release consisting of mercury dissolution in oral fluids followed by partial ionization and partial evaporation of the released mercury. In this project period the research is focused on the role of the oxide on the surface of the silver-mercury (gamma1) matrix phase of dental amalgam, which is the main source of released mercury, as a barrier to mercury release. The Specific Aims in the proposed project period include determination of the kinetics of the tin oxide growth on the gamma1 phase as a function of the tin content in the gamma1 phase and the pH of the environment, determination of the kinetics of mercury dissolution as a function of the tin oxide film thickness and tin oxide dissolution rate, determination of the effect of indium dissolved in the gamma1 phase on the oxide film characteristics and mercury release, and determination of the effect of brushing on the thickness of the tin oxide and the mercury release. The proposed work is based on the quantitative models developed to date. The research will be performed in vitro using laboratory-prepared specimens of the gamma1 phase containing various amounts of tin and indium. It will involve in situ electrochemical determination of the oxide thickness, cold- vapor atomic absorption spectrophotometry for dissolved mercury analysis, and various electrochemical techniques to characterize the behavior of the specimens in synthetic oral fluids. The results will provide information necessary for the development of dental amalgams, which form quickly an effective surface barrier to mercury release.